1. Field of the Invention
This application claims priority from Japanese Patent Appln. No. 2004-299254, filed Oct. 13, 2004, the contents of which are herein incorporated by reference in their entirety.
The present invention relates to a producing method of a wired circuit board and, more particularly, to a method of producing a wired circuit board while conveying an elongate base material using rolls.
2. Description of the Prior Art
As is known, the roll-to-roll process is used for forming a conductive pattern and the like on a surface of elongate base material while conveying the elongate base material by using rolls, in order to provide an improved production efficiency of the wired circuit board.
Along with the trend toward lighter, thinner, and more compact electronic components, the trend in wired circuit boards is also toward thinner profile. A thin, elongate, base material is however creased or get wrinkled when conveyed using rolls. Prior art proposes an attempt solution to prevent this that a carrier film is adhesively bonded to a surface of a thin, copper clad laminate (e.g. JP Laid-open (Unexamined) Patent Publication No. Hei 6-132628).
Also, prior art proposes improvement of the process of coating a photosensitive solder resist using a roll coater, to prevent adhesion of foreign matter to a surface of the photosensitive solder resist. In the improvement, after the resist layer is dried to volatilize solvent components of the resist layer, a light-transparency protecting film is laminated on the resist layer and a solder resist pattern is provided on the surface of the protecting film. Then, after the resulting resist layer is exposed to light, the protecting film is removed from the resist layer and the resist layer is developed (e.g. JP Laid-open (Unexamined) Patent Publication No. 2004-79844).
Meanwhile, along with improvements in fine conductive pattern in recent years, the additive process of forming a conductive pattern by electrolytic plating is in widespread use. However, when the conductive pattern is formed on the base material by the electrolytic plating, the following problems occur. In general, in the electrolytic plating, a current density becomes higher at both widthwise end portions of the elongate base material than at a widthwise central portion of the same. Due to this, deposition of the electrolytic plating is promoted at the both widthwise end portions of the elongate base material, so that thickness of the conductive pattern plated is apt to become larger at the both widthwise end portions of the elongate base material than at the widthwise central portion of the same.
When this elongate base material is coated with the photosensitive solder resist to cover the conductive pattern by the roll coater, the conductive pattern formed to have a larger thickness at the both widthwise end portions of the elongate base material is brought into contact with the roll coater, to cause meander of the elongate base material conveyed with the rollers disadvantageously.
Also, when the protecting film is laminated on the surface of the photosensitive solder resist, the elongate base material and protecting film is conveyed while being held in sandwich relation between a pair of upper and lower nip rollers and being pressurized by the nip rollers. When the conductive pattern has a larger thickness at the both widthwise end portions of the elongate base material than at the widthwise central portion of the same, the pressure cannot be uniformly applied on the elongate base material including portions thereof close to the both ends thereof, to cause entry of air bubbles in between the photosensitive solder resist and the protecting film. This will cause scattering of light in the subsequent exposure process, and as such can cause production of pinholes in the subsequent development process disadvantageously.